Lightning arrester with semiconductor electrodes



June 27, 1967 H, GREBER 3,328,631

LIGHTNING ARRESTER WITH SEMICONDUCTOR ELECTRODES Filed June 8, 1965llllllllllllllll, {/maw INVENTOR United States Patent 3,328,631LIGHTNING ARRESTER WITH SEMICONDUCTOR ELECTRODES Henry Greber, 225 W.80th St., Apt. 8D, New York, N.Y. 10024 Filed June 8, 1965, Ser. No.462,375 4 Claims. (Cl. 31536) ABSTRACT OF THE DISCLOSURE This lightningarrester consists of a series of gaps between disc-shaped electrodesmade of semiconducting material, such as Carborundum, graphite, carbon,with each disc serving as an electrode of a gap and also as a resistancein series with this gap, in addition, each disc is provided with agroove along its periphery, where the air between the Walls of saidgroove is broken down electrically when the voltage drop in the discsurpasses the breakdown voltage of gap between the walls of the groove,so that said disc is then bypassed with an arc.

The purpose of this invention is to provide a simple lightning arresterof shorter duration of the discharge voltage-as the voltage drop on thelightning arrester during its discharge is being called-in comparison tothat of lightning arresters known in the art. It is common knowledge,that the characteristic, which is the curve showing the duration of anovervoltage in function of its value, of a lightning gap is moreconvenient than that of lightning arrester. For a lightning gap, theovervoltage due to a lightning stroke rises quickly, until the gap isbridged by an arc. From this moment, at which the discharge through thegap begins, the overvoltage falls rapidly to zero. In contrast, in .alightning arrester, when the fast rising overvoltage causes thedischarge through this device, the large voltage drop on the arresterlasts for a while, and only gradually falls down to zero. Even thoughthe duration of the discharge voltage on the lightning arrester amountsonly to a few microseconds, an insulation breakdown of the equipmentprotected by this lightning arrester may take place during this time.This is so because the longer the duration of a given voltage surge, thesmaller its value that can be withstood by the insulation. Another, notless important objective of this invention is to provide a lightningarrester whose electrodes would be free from corrosion, in spite of itshousing not being hermetically sealed from the ambient air. A furtherpurpose of this lightning arrester with semiconductor electrodes is theuniform distribution of the voltage on its internal gaps. The lastobjective is achieved by means of resistance grading, which in this caseconsis-ts in application of tubular spacers of high resistance, placedbetween the internal gaps. The first objective is achieved by usingelectrodes of semiconductor material, such as Carborundum, graphite orcarbon with proper binders, for the electrodes of the discharge gaps.These electrodes, in form of discs play a dual role. While serving aselectrodes of the gaps, they also function as semiconductor resistorsconnected in series with the gaps. Since these electrodes are made ofsemiconductor material, they, naturally, are not subject to corrosion.Hence, there is no need to seal hermetically the housing of thelightning arrester. The lack of such sealing not only simplifies thedesign of the lightning arrester, but also reduces its cost. To make thecharacteristic of the lightning arrester resemble that of a simple gap,the semiconductor dis-cs, mentioned above, are provided with groovesrunning along their circumferences. If only one groove per disc is used,this groove is placed about in the middle of the height of the disc. Thehorizontal sidings of such 3,3286'3]. Patented June 27, 1967 channelserve as additional gaps, which are broken down when the voltage dropalong a disc surpassed the breakdown voltage between the horizontal sidewalls of the groove.

In FIGURE 1 is shown a longitudinal cross section of the lightningarrester in its usual vertical position. Porcelain tube 1, provided withthe three skirts 2, has threads 3 on both of its ends. Also porcelaintube 4, has such threads 5, and skirts 6. The two tubes (1 and 4) areconnected by means of porcelain coupling 7, which is threaded on itsinternal surface. The lower end of tube 4, is closed by means of metalcap, which also has a thread on its internal surface, that fits tothread 5 of tube 4. Metallic cap 8 is linked to ground 10, by means ofwire 9. The last two items are shown diagrammatically. Porcelain tubes 1and 4 contain eight semiconductor discs numbered 11, 12, 13, 14, 15, 16,17, and 18. These discs are separated with tubular spacers designatedwith the numerals: 19, 20, 21, 22, 23, 24, all made of ceramic materialcontaining conductive additives such as Carborundum, graphite, orcarbon. In detailed consideration of disc 15, for example, as arepresentative of all other discs 11, 12, 13, 14, 16, 17, and 18, whichare all exactly alike, it can be seen that it has its terminal surfacesbeveled, 25 and 26. It can also be seen that said disc has groove 27,cut along its vertical circumference, about in the middle of its height."In FIGURE 1, only one groove per dis-c is shown, for the sake ofsimplicity. In actuality, several such channels per disc may be employed. The bottom disc 18 is in direct contact with the metallic cap 8,and through it with ground 10. The upper disc 11 is connected to theprotected phase conductor, which is not shown, since it is not a part ofthis lightning arrester. This connection is made through wire 28, whichis provided with the Wide lug 29. This lug is pressed towards disc 11 bymeans of spring 30. The top of the lightning arrester is closed byporcelain cap 31, which is provided with thread 32 fitting to thread 3of porcelain tube 1. It can be seen that cap 31 is provided with channel33, through which wire 28 is brought out. Cap 31 is not hermetic, andfits loosely on tube 1, through the intermediary of threads 3 and 32. Noattempt is made to prevent insects from entering into cap 31 throughchannel 33, since these creatures could in no way influence thefunctioning of the lightning arrester.

In operation of this lightning arrester, the overvoltage appearingbetween wire 28 and ground 10, in consequence of a lightning stroke tothe protected phase conductor, distributes itself evenly on the gapsformed by the consecutive semiconductor discs. The uniform voltagedistribution over the gaps is enforced by the tubular spacers, whichthough made of ceramic material with little conductive additives, sothat they can be considered as being insulators, are at the same timeresistors inserted in series with the gaps. At a certain value of theovervoltage caused by lightning stroke, or by switching, the gapsbetween the discs 11 and 12, 12 and 13, 13 and 14, 15 and 16, 16 and 17,17 and 18, are overbridged with arcs. If the intensity of the dischargecurrent is not too great, the overcharge will flow to ground throughthese arcs. They will be extinguished as soon as the overcharge willhave passed, and the resistance of the semiconductor discs will preventthe follow current from flowing through the arrester. In case of greatintensity of the discharge current, the voltage drop on each disc willbe considerable, and delay the discharge through the lightning arrester.It looks as if the overcharge were dammed up in front of the lightningarrester, which because of the resistance of its semiconductor discs,would let this overcharge flow to ground only gradually. The longer theovercharge is piled up ahead of the lightning arrester, and has to waitto be discharged to ground,

the greater is the danger of dielectric breakdown of the insulation ofthe electric equipment to be protected. Therefore, at great intensity ofthe discharge current, the discs themselves are shunted with gaps. Theseconsist, for simplicity, in channels cut along the circumferences of thediscs. As soon as the magnitude of the discharge current drops, the arcswithin the channels of the discs are extinguished, so that the fullresistance of the discs is inserted into the circuit through thelightning arrester.

It is obvious that the grooves in the semiconductor discs can bereplaced with metallic electrodes forming gaps around the discs. Howeverin this invention, the use of metallic electrodes is consistentlyavoided, in order to avoid corrosion of such electrodes. Also many othermodifications and variations of this invention can be made within itsconcept as defined by the following claims.

I claim:

1. A lighting arrester with semiconductor electrodes consisting of aseries of semiconductor discs with high resistivity spacers between themarranged so that discharge gaps are maintained between said discs, witheach disc having at least one groove out along the circumference of itsvertical wall, said discs being arranged so that the top disc isconnected to the protected phase conductor and the bottom disc isconnected to ground.

2. A lightning arrester as in claim 1, with said semiconductors discshaving beveled edges of their top and bottom horizontal surfaces.

3. A lightning arrester as in claim 1, with a housing consisting ofseveral porcelain tubes, provided with skirts and threads on both oftheir ends, said tubes being connected to each other :by means ofporcelain couplings having threads on their interal surfaces.

4. A lightning arrester as in claim 1, with said spacers made of ceramicmaterial with conductive additive of Carborundum added in suchproportion that the resistance of said spacer would amount to about onethousandths of the resistance of said semiconductor disc.

References Cited UNITED STATES PATENTS 1,778,829 10/1930 Harrington3l33l1 2,151,559 3/1939 M-cEachron 315-36 2,891,194 6/1959 McStrack 31536 DAVID J. GALVIN, Primary Examiner.

1. A LIGHTING ARRESTER WITH SEMICONDUCTOR ELECTRODES CONSISTING OF ASERIES OF SEMICONDUCTOR DISCS WITH HIGH RESISTIVITY SPACERS BETWEEN THEMARRANGED SO THAT DISCHARGE GAPS ARE MAINTAINED BETWEEN SAID DISCS, WITHEACH DISC HAVING AT LEAST ONE GROOVE CUT ALONG THE CIRCUMFERENCE OF ITSVERTICAL WALL, SAID DISCS BEING ARRANGED SO THAT THE TOP DISC ISCONNECTED TO THE PROTECTED PHASE CONDUCTOR AND THE BOTTOM DISC ISCONNECTED TO GROUND.